It is well-known that the addition products of an alkylene oxide and a mercaptan or hydrogen sulfide can be used, for example, in diesel fuels to improve octane number, as a surfactant for industrial applications, as an additive for transmission fluids, as lubricating oil additive, and as an insecticide such as fly repellents. Conventionally, the addition products or alkoxylated thio-compounds, are produced by reacting an alkylene oxide with a mercaptan or hydrogen sulfide catalyzed by an alkaline catalyst such as a hydroxide of an alkali metal or a hydroxide of an alkaline earth metal or an alkyl-substituted ammonium hydroxide. See U.S. Pat. Nos. 2,570,050 and 2,570,051. An alkaline catalyst such as sodium hydroxide in methanol has also been used as a catalyst for the reaction of an alkylene oxide and mercaptan. See U.S. Pat. No. 3,775,483.
The above-described processes, however, was found to have a lag period, i.e., no reaction initially, especially at low temperatures, i.e., lower than about 70.degree. C. Consequently, more alkylene oxide needs to be added to the reaction mixture to initiate the reaction. However, the excess amount of alkylene oxide added generally causes too vigorous and too exothermic reactions. A "too vigorous" reaction is one that the reaction mixture boils out of reactor and a "too exothermic" reaction is one that the temperatures of the reaction cannot be maintained below the highest temperature that is permissible. This too vigorous and too exothermic reaction is termed herein as runaway reaction. In order to avoid this runaway reaction so that a process can be carried out at lower temperatures to obtain a greater selectivity toward the desired product, a new process needs to be developed.